Question: Which of these numbers is composite? ${11,\ 17,\ 55,\ 83,\ 97}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 11, 17, 83, and 97 each have only two factors. The factors of 55 are 1, 5, 11, and 55. Thus, 55 is the composite number.